The present invention relates to a method pertaining to synchronous radio transmission. More specifically, the invention relates to a method for synchronous transmission over a frequency band where asynchronous transmission rules are applied. The synchronous radio system may be a DECT-type system, i.e. a relatively short-range cordless personal communication system, which shall be adapted with comply to the rules for asynchronous transmission, for instance a so-called packet-switched data transmission with retained synchronism.
In radio communication technology it is common to distinguish between asynchronous and synchronous transmission.
Traditionally, radio communication has been developed for circuit-switched synchronous services, such as mobile telephones and cordless telephones for speech communication and ISDN services. A common feature of these types of system is that information is transmitted to a given receiver within given specific time points in a time-divided system or over a certain radio frequency, a frequency-divided system. An example of time-divided systems are the so-called TDMA systems (Time Division Multiple Access), in which information is transmitted in time slots with determined periodic time spacing for each channel.
Radio systems using asynchronous transmission normally utilize so-called packet switching over a certain radio frequency, although these packets are transmitted and received totally at random from one transmitter-receiver to another transmitter-receiver.
An example of asynchronous systems is found in so-called Local Area Data Networks, which utilize packet-data switching via radio instead of via a circuit-switched radio medium.
A certain frequency spectrum has been reserved for asynchronous radio transmission (e.g. a frequency spectrum of 1910-1920 MHz allocated by the Federal Commission, FCC, in the U.S.A.). This enables short access times to be obtained for asynchronous packet transmission.
In asynchronous transmission, several users share the same frequency spectrum thereby obviating the need for frequency planning. Collision occurs at times resulting in a congestion in the network between two users, although the intended data packet is retransmitted. The retransmission of data packets at certain time points after transmitting an asynchronous data packet is known to the art; see for instance the disclosures made in SE-A-9302067-5.
Synchronous or periodic transmission involves sending and receiving information at predetermined time points and/or over certain determined frequencies, as in the case of the TDMA systems mentioned in the introduction. In the case of the above example from American standards having a frequency band of between 1910 and 1920 MHz in the case of asynchronous transmission, a band between 1920 and 1930 MHz is intended for synchronous transmission. These two bands shall thus be used separately of one another.